The present invention generally relates to an intravenous cardiac lead and method having an improved configuration for fixing the lead in a desired position within a vein or an artery after implantation. The present invention is more particularly directed to such an intravenous lead for use with an implantable atrial defibrillator which provides cardioverting electrical energy to the atria of the heart when the heart is in need of cardioversion. The intravenous cardiac lead of the present invention is particularly adapted for implantation in the coronary sinus or the coronary sinus and the great cardiac vein of the heart and includes at least one electrode adapted to be within the coronary sinus or great vein of the heart and a second electrode adapted to be within the right atrium of the heart when the lead is fed into the heart to a preferred position to enable the sensing of atrial activity of the heart and the delivery of the cardioverting electrical energy to the atria.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. In addition, patients afflicted with atrial fibrillation generally experience palpitations of the heart and may even experience dizziness or even loss of consciousness.
Atrial fibrillation occurs suddenly and many times can only be corrected by a discharge of electrical energy to the heart through the skin of the patient by way of an external defibrillator of the type well known in the art. This treatment is commonly referred to as synchronized cardioversion and, as its name implies, involves applying electrical defibrillating energy to the heart in synchronism with a detected ventricular electrical activation (R wave) of the heart. The treatment is very painful and, unfortunately, most often only results in temporary relief for patients, lasting but a few weeks.
Drugs are available for reducing the incidence of atrial fibrillation. However, these drugs have many side effects and many patients are resistant to them which greatly reduces their therapeutic effect.
Implantable atrial defibrillators have been proposed to provide patients suffering from occurrences of atrial fibrillation with relief. Unfortunately, to the detriment of such patients, none of these atrial defibrillators have become a commercial reality.
Two such proposed defibrillators, although represented as being implantable, were not fully automatic, requiring human interaction for cardioverting or defibrillating the heart. Both of these proposed defibrillators require the patient to recognize the symptoms of atrial fibrillation with one defibrillator requiring a visit to a physician to activate the defibrillator and the other defibrillator requiring the patient to activate the defibrillator with an external magnet.
An improved implantable atrial defibrillator and lead system which exhibits automatic operation is fully described in U.S. Pat. No. 5,282,837, issued Feb. 1, 1994, in the names of John M. Adams and Clifton A. Alferness for ATRIAL DEFIBRILLATOR AND METHOD, which patent is assigned to the assignee of the present invention and is incorporated herein by reference. The atrial defibrillator disclosed in the aforementioned referenced patent is truly automatic by including an atrial fibrillation detector which, responsive to sensed atrial activity, determines when the atria of the heart are in need of cardioversion. When the atrial fibrillation detector determines that the atria are in fibrillation and thus in need of cardioversion, the atrial fibrillation detector causes a cardioverter stage to deliver defibrillating or cardioverting electrical energy to the atria in timed relation to a detected ventricular electrical activation (R wave) of the heart. As a result, the atria are automatically and safely cardioverted.
As also disclosed in the aforementioned cross-referenced application, the quantity of electrical energy which is required to cardiovert or defibrillate the atria is reduced by an intravenous lead having an electrode adapted to be within the right atrium and another electrode adapted to be within the coronary sinus or the great cardiac vein beneath the left atrium. The application of the cardioverting electrical energy across these electrodes not only reduces the energy required to cardiovert the atria, but also reduces the amount of energy applied to the ventricles. To place the electrodes in the positions noted above, the lead is fed down the superior vena cava, into the right atrium, through the coronary sinus ostium, and advanced into the coronary sinus and the great cardiac vein. The lead is also preformed to generally conform to the shape of the coronary sinus and great vein to assist in holding the lead in place after implantation.
While the above-mentioned lead is preshaped to conform to the lead feed path to assist in holding the lead in place after implantation, it is desirable to provide the lead with more positive fixation since the blood flow through the coronary sinus is in a direction which tends to force the lead in a direction reverse to the feed path and out of the coronary sinus. Such positive fixation, however, must permit adequate blood flow through the coronary sinus and not cause occlusions.
U.S. application Ser. No. 08/147,330, filed Nov. 3, 1993, in the names of Clifton A. Alferness and John R. Helland, for INTRAVENOUS CARDIAC LEAD WITH IMPROVED FIXATION AND METHOD, now U.S. Pat. No. 5,387,233 , assigned to the assignee of the present invention and incorporated herein by reference, describes an intravenous lead and method of implanting the same which provides such positive fixation. Fixation of the lead is provided by a preformed section of the lead which has a resiliently coiled configuration. After the lead is implanted within a vein or an artery, such as the coronary sinus or the coronary sinus and great cardiac vein, the preformed section is permitted to assume its coiled configuration for making substantially continuous surface contact with inner wall surfaces of the coronary sinus or great vein in the region of the coiled section. Such surface contact fixes the lead in place. Thereafter, fibrous tissue which builds up around the lead assures permanent fixation.
While the lead and method of the copending application mentioned above provides an elegant solution for fixing an intravenous lead within an artery or vein, such as the coronary sinus or the coronary sinus and great cardiac vein, a further refinement has been realized. This further refinement provides additional assurance that the lead will remain in a fixed position after implantation.
As is well known in the art, electrode or lead migration after implantation can have serious consequences in both being able to sense heart activity and effectively provide therapy to the patient. Loss of electrogram signals needed for diagnosis can occur and energy thresholds for providing needed therapy can become excessively high. Hence, any improvement towards electrode and lead fixation is important.